Organic electroluminescent device

ABSTRACT

The present invention relates to an organic electroluminescent device comprising a substrate ( 40 ) and on top of the substrate ( 40 ) a substrate electrode ( 20 ), a counter electrode ( 30 ) and an electroluminescent layer stack ( 50 ) with at least one organic electroluminescent layer arranged between the substrate electrode ( 20 ) and the counter electrode ( 30 ), an encapsulation means ( 90 ) encapsulating at least the electroluminescent layer stack ( 50 ) and at least one non-conductive spacer means ( 70 ) arranged on the substrate electrode ( 20 ) to mechanically support the encapsulation means ( 90 ) and to prevent an electrical short between the substrate electrode ( 20 ) and the counter electrode ( 30 ) during the mechanical support, wherein the spacer means ( 70 ) comprise at least one light scattering means ( 80 ) for redirecting at least a part of light ( 65 ) trapped in the substrate ( 40 ), to a method of manufacturing such an encapsulated electroluminescent device and to the use of an array, preferably a hexagonal array, of non-conductive spacer means.

FIELD OF THE INVENTION

The present invention relates to an organic electroluminescent deviceencapsulated by an encapsulation means, a method of manufacturing suchan encapsulated electroluminescent device and the use of an array ofalmost invisible spacer means to support the electroluminescent device.

BACKGROUND OF THE INVENTION

Common organic electroluminescent devices (OLEDs) comprise a functionallayer stack on top of a substrate with at least one organicelectroluminescent layer sandwiched between a substrate and a counterelectrode, whereas parts of the electroluminescent layer and/or parts ofthe counter electrode are sensitive to water and/or oxygen. ThereforeOLEDs are encapsulated by cover lids to prevent ambient substance suchas water and oxygen from reaching the functional layers, to provide OLEDdevices having a sufficient lifetime. The cover lid defines anencapsulated volume around the functional layer stack with typically agap or space between the outermost layer of the functional layer stackand the inner side of the cover lid. This gap or space may be filledwith inert gas, e.g. dry nitrogen.

A problem of OLEDs encapsulated with a cover lid is the mechanicalstability of this encapsulation. Pressure differences in the surroundingenvironment may give rise to substantially deformations in the coverlid, especially in case of large area OLED devices. The deformations ofthe cover lid may be so high, that the cover lid touches the functionallayer stack of the OLED device causing failures, e.g. shorts, of theOLED device.

Document WO2009001241 discloses an OLED encapsulated with a cover lidcomprising shunting structures forming a grid of linear non-transparentmetallic stripes to obtain a more homogeneous voltage distributionacross the substrate electrode, where each metallic strip extends overthe complete lengths of the substrate electrode. Each shunting stripe iscompletely covered by a smooth non-conductive structure to facilitatethe formation of a continuous organic layer and counter electrode layerthereon. The resulting grid of non-conductive structures on top of theshunting structures simultaneously serves as spacer structurespreventing electrical shorts between the counter electrode and thesubstrate electrode as a result of mechanical contact between the lidand the functional layer stack. However, the OLED area covered by thespacer structures and non-transparent shunting structures does not emitlight and thus is visible as a disturbing grid of black lines. Thepresence of black lines prevents a homogeneous brightness distributionover the whole light emitting area of the OLED device.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an organicelectroluminescent device with a spacer structure preventing electricalshorts between both electrode as a result of mechanical contact betweenthe cover lid and the functional layer stack with a more homogeneousbrightness distribution and an improved light emission.

This object is solved by an electroluminescent device comprising asubstrate and on top of the substrate a substrate electrode, a counterelectrode and an electroluminescent layer stack with at least oneorganic electroluminescent layer arranged between the substrateelectrode and the counter electrode, an encapsulation meansencapsulating at least the electroluminescent layer stack and at leastone non-conductive spacer means arranged on the substrate electrode tomechanically support the encapsulation means and to prevent anelectrical short between the substrate electrode and the counterelectrode during the mechanical support, wherein the spacer meanscomprise at least one light scattering means for redirecting at least apart of light trapped in the substrate.

The leading idea of the present invention is to make the spacer means,which provide mechanical support to the encapsulation means, lessvisible, preferably invisible, for the viewer of the electroluminescentdevice by redirecting light trapped in the substrate from the areacovered by the spacer means towards the substrate surface in order tocouple out at least a part of the trapped light to the environment fromareas covered by the spacer means. The spacer means itself may betransparent or opaque. The area to which the non-conductive spacer meansis applied may appear dark at normal operation of the electroluminescentdevice, since charge injection from the substrate electrode to theelectroluminescent layer stack is blocked. The spacer means compriseslight scattering means for scattering light generated by the organicelectroluminescent layer. The light scattering means may comprise lightscattering particles and/or flakes embedded in the spacer means. Thislight scattering means scatters and or reflects part of the artificiallight guided inside the substrate. This results in a brightening of theotherwise non-emissive area. As the substrate often works as a kind oflight guide, the scattering means of the protective means enables thislight to be scattered and reflected out of the electroluminescentdevice. The resulting electroluminescent device (OLED) shows a morehomogeneous brightness distribution. The scattering properties togetherwith the size of the substrate electrode area covered by each spacermeans can be adapted to achieve a homogeneous brightness distributionwith almost invisible spacer means. Less visible or invisible spacermeans can support the encapsulation means more effective, because thenumber of spacer means, preferably spacer means covering small areas,may be adapted (increased) to the size and shape of the encapsulationmeans without disturbing the visual appearance (homogeneous brightness)of the electroluminescent device.

In the context of the invention the notion electroluminescent (EL) layerstack denotes all layers prepared between the substrate electrode andthe counter electrode. In one embodiment of an EL layer stack, itcomprises at least one light emitting organic electroluminescent layerprepared between substrate and counter electrode. In other embodimentsthe layer stacks may comprise several layers prepared between substrateand counter electrode. The several layers may be organic layers, such asone or more hole transport layers, electron blocking layers, electrontransport layers, hole blocking layers, emitter layers or a combinationof organic and non-organic layers. The non-organic layers may beadditional electrodes in case of two or more light emitting layerswithin the layer stack and/or charge injection layers. In a preferredembodiment the substrate electrode and or the counter electrode compriseat least one of the following materials: ITO, aluminum, silver, dopedZnO or an oxide layer.

In the context of the invention the notion substrate denotes a basematerial onto which the different layers of an electroluminescent deviceare deposited. Normally, the substrate is transparent and is made ofglass. Furthermore, it may be preferable that the substrate istransparent, preferably comprising at least one of the followingmaterials: silver, gold, glasses or ceramics. It may also be atransparent polymer sheets or foils with a suitable moisture and oxygenbarrier to essentially prevent moisture and/or oxygen entering theelectroluminescent device layer stack. It is also possible to usenon-transparent materials like metal foils as substrate. The substratemay comprise further layers, e.g. for optical purposes like lightout-coupling enhancement or other purposes. The substrate is usuallyflat, but it may also be shaped into any three-dimensional shape that isdesired.

In the context of the invention the notion substrate electrode denotesan electrode deposited on top of the substrate. Usually it consists oftransparent ITO (Indium-Tin oxide) optionally with an undercoating ofSiO₂ or SiO to suppress diffusion of mobile atoms or ions from the glassinto the electrode. For a glass substrate with an ITO electrode, the ITOis usually the anode, but in special cases it can also be used as thecathode. In some cases, thin Ag or Au layers (8-15 nm thick) are usedsingle or in combination with ITO as the substrate electrode. If a metalfoil is used as the substrate, it takes also the role of the substrateelectrode, either anode or cathode. The notation on-top-of denoted thesequence of the listed layers. This notation explicitly comprises thepossibility of further layers in between the layer denoted as on top ofeach other. For example, there might be additional optical layers toenhance the light out-coupling arranged between substrate electrode andsubstrate.

In the context of the invention the notion counter electrode denotes anelectrode away from the substrate. It is usually non-transparent andmade of Al or Ag layers of sufficient thickness such that the electrodeis reflecting (typically 100 nm for Al and 100-200 nm for Ag). It isusually the cathode, but it can also be biased as the anode. Fortop-emitting or transparent electroluminescent devices the counterelectrode has to be transparent. Transparent counter electrodes are madeof thin Ag or Al layers (5-15 nm) or of ITO layers deposited on top ofthe other previously deposited layers.

In the context of the invention an electroluminescent device with acombination of a transparent substrate, a transparent substrateelectrode and a non-transparent counter electrode (usually reflective),emitting the light through the substrate is called “bottom-emitting”. Incase of electroluminescent device comprising further electrodes, incertain embodiments both substrate and counter electrodes could be botheither anodes or cathodes, when the inner electrodes as driven ascathodes or anodes. Furthermore, in the context of the invention anelectroluminescent device with a combination of a non-transparentsubstrate electrode and a transparent counter electrode, emitting thelight through the counter electrode is called “top-emitting”.

In the context of the invention the notion transparentelectroluminescent device denotes an electroluminescent device, wherethe substrate, the substrate electrode, the counter electrode and theencapsulation means are transparent. Here the electroluminescent deviceis both, bottom and top-emitting. In the context of the invention alayer, substrate or electrode is called transparent if the transmissionof light in the visible range is more than 50%; the rest being absorbedor reflected. Furthermore, in the context of the invention a layer,substrate or electrode is called semi-transparent if the transmission oflight in the visible range is between 10% and 50%; the rest beingabsorbed or reflected. In addition, in the context of the inventionlight is called visible light, when it possesses a wavelength between450 nm and 650 nm. In the context of the invention light is calledartificial light, when it is emitted by the organic electroluminescentlayer of the electroluminescent device.

Furthermore, in the context of the invention a layer, connector orconstruction element of an electroluminescent device is calledelectrically conducting if its electrical resistance is less than 100000Ohm. In the context of the invention passive electronic componentscomprise resistors, capacitors and inductivities. Furthermore, in thecontext of the invention active electronic components comprise diodes,transistors and all types of integrated circuits.

In the context of the invention a layer, substrate, electrode or aconstruction element of an electroluminescent device is calledreflective if light incident on its interface is returned according tothe law of reflection: the macroscopic angle of incidence equals themacroscopic angle of reflection. Also the term specular reflection isused in this case. Furthermore, in the context of the invention a layer,substrate, electrode or a construction element of an electroluminescentdevice is called scattering if light incident on it is not returnedaccording to the law of reflection: macroscopic angle of incidence isnot equal to the macroscopic angle of the returned light. There is alsoa distribution of angles for the returned light. Instead of scattering,the term diffuse reflection is also used.

In the context of this invention the encapsulation means encapsulates atleast the electroluminescent layer stack. The encapsulation means mayalso encapsulate the whole stack of layers of the electroluminescentdevice or just a plurality of layers, forming a part of the whole stackof layers. Preferably, the encapsulation means is a gas-tight element,covering at least the organic electroluminescent layer and the counterelectrode. By using a gas-tight encapsulation means, it is preventedthat environmental factors like water, or oxygen can damage theencapsulated layers. The encapsulation means may form a gas-tight lid.This lid may be formed of glass or metal. It is also possible to formthe encapsulation means by one or a plurality of layers applied to theelectroluminescent device or just parts of it. The layers may comprisesilicon, silicon oxide, silicon nitride, aluminum oxide or siliconoxinitride. All the named encapsulation means prevent mechanical and/orenvironmental factors from affecting the layer stack of theelectroluminescent device adversely. Additional getter materials may bearranged inside the encapsulated volume, preferably attached to theinner side of the encapsulation means, to further reduce the amount ofwater and/or oxygen inside the encapsulated device. As an example, theencapsulation means can be made of metals, glass, ceramics orcombinations of these. It is attached to the substrate by conductive ornon-conductive glue, melted glass frit or metal solder.

In an embodiment the sum of all areas covered by spacer means on top ofthe substrate electrode is significantly smaller than the area coveredby the electroluminescent layer stack, preferably less than 10% of thearea covered by the electroluminescent layer stack, more preferably lessthan 5% of the area covered by the electroluminescent layer stack, evenmore preferably less than 1% of the area covered by theelectroluminescent layer stack. From areas covered by non-conductivespacer means no current is injected into the electroluminescent layerstack preventing the generation of light within the electroluminescentlayer stack on top of the spacer means. A smaller sum of all areas(=total area) covered by spacer means improves the total brightness ofthe electroluminescent device, because the active area of theelectroluminescent layer generating light is larger. In a preferredembodiment the largest extension of the area covered by the spacer meansis significantly smaller than each of the lateral extensions of the areacovered by the electroluminescent layer stack, preferably less than 10%of each of the lateral extensions of the area covered by theelectroluminescent layer stack, more preferably less than 5% of each ofthe lateral extensions of the area covered by the electroluminescentlayer stack, even more preferably less than 1% of each of the lateralextensions of the area covered by the electroluminescent layer stack.The extension of the area covered by the spacer means denotes thedistance two points at the outer edge of area of the spacer means. Thelargest extension is the maximum possible distance between such twopoints. As an example, the largest extension of a circle-like area isthe diameter of this area. A number of small spacer means occupying acorresponding small area on top of the substrate electrode will provideat least the same sufficient support to the encapsulation means comparedto a lower number of spacer means occupying a larger area per spacermeans. However, it is much easier to make the spacer means with smallerlateral extension less visible, preferably non-visible, by addingscattering particles, because the required scattering effect to achievea more homogeneous brightness, preferably a homogeneous brightness, ofthe OLED device is easier to be adjusted for a area with smaller lateralextensions. As an example, s small covered area with a large extensionin one dimension may be still visible as a thin dark line compared tothe bright surrounding areas, while the same small area with a shapewith small lateral extension in both dimensions can be made lesservisible or even invisible.

In another embodiment the electroluminescent device comprises an arrayof spacer means, preferably a regular array, more preferred a hexagonalarray. An array of spacer means will provide a more secure support tothe encapsulation means compared to a single spacer means, as an examplelocated somewhere in the middle of the light emitting area. Anon-visible array of spacer means can be achieved easier with a regulararray, most easy with a hexagonal array, which to the human eye is lessvisible than other arrays.

In another embodiment the height of the spacer means ranges between 5and 1000 micrometer, preferably between 10 and 500 micrometer, morepreferred between 10 and 200 micrometer, even more preferred between 10and 100 micrometer, to provide sufficient support to the encapsulationmeans. The layer stack on top of the substrate electrode comprisingelectroluminescent layer stack and counter electrode has a typicalthickness of 200-300 nm. The encapsulation means has to be fixed to thesubstrate electrode in a gas-tight manner with suitable fixation means,e.g. glue, glass frit, or metallic solder, having a height of at least afew micrometers. To provide a sufficient support of the encapsulationmeans require spacer means of heights at least in the micrometer range.

It is advantageous to use an encapsulation means with a gap betweensubstrate electrode and inner side of the encapsulation means in therange between a few micrometers and a few hundreds of micrometers inorder to achieve a thin electroluminescent device, where simultaneouslythe spacer means with heights comparable to said gap prevent theencapsulation means from touching the counter electrode somewherebetween the spacer means and protect the counter electrode from gettinginto electrical contact with the substrate electrode in case ofmechanical contacts between encapsulation means and counter electrodeabove the spacer means. To fulfill these tasks, the spacer means must bethick and hard enough. The precise thickness and hardness depend on theactual pressure exerted by the encapsulation means and the present gapbetween encapsulation means and substrate electrode. In a preferredembodiment the height of the spacer means is adapted to be essentiallythe same as the distance between the counter electrode and the innerside of the encapsulation means as present outside the area covered withspacer means, preferably the encapsulation means is a flat lid. Peopleskilled in the art are able to choose the required thickness of thespacer means within the scope of this invention depending on the layerthicknesses and the geometrical shape of the encapsulation means. Inthis embodiment, the spacer means not only prevent electrical contactsbetween both electrodes but also provide a strong mechanical support tothe encapsulation means by carrying the encapsulation means. Here theencapsulation means may be manufactured from more fragile material orthinner material, e.g. thin glass back plates sealed to the substratewith glass frit, glue or metallic solder.

In another embodiment the spacer means comprises at least one of thefollowing materials: non-conductive glue, a photo resist, a lacquer,paint or a layer of glass, made of re-melted glass frit or combinationsthereof. The spacer means has to simultaneously mechanically support theencapsulation means and to prevent the direct contact between thecounter electrode and the substrate electrode, which would lead to ashort. The named materials provide the required hardness to support theencapsulation means to protect the substrate electrode and can easily beapplied to the substrate electrode, often without the need of a vacuumchamber. Therefore, the application of the spacer means can be doneeasily and economically. People skilled in the art may choose otherelectrically non-conductive materials within the scope of thisinvention. Non-conductive glue has the advantage, that it is easy toapply and will not damage the substrate electrode. Non-conductive glueis mostly a viscous fluid, which can easily be attached to the substrateelectrode. Furthermore, it can be applied at ambient pressure and thereis no need to use a vacuum chamber. Therefore, a drop of non-conductiveglue can easily be applied to the substrate electrode and prevent as aspacer means any short between the two electrodes. To achieve lastingnon-conductive glue at least one of the following matrices may be used:epoxys, polyurethanes, acrylic or silicone.

Preferably the non-conductive glue of the spacer means is anhydrousand/or water free. In the context of the invention, the notion waterfree and/or anhydrous describes the fact, that no degradation due towater content during the average lifetime of an electroluminescentdevice can be observed by the naked eye. A visible degradation of theorganic electroluminescent layer due to water diffusing into the layerstack can take the form of growing black spots or shrinkage of theemissive region from the edges. The notion water free and/or anhydrousnot only depends on the non-conductive glue itself but also on theamount of water, which can be absorbed by the organic electroluminescentlayer without damaging it. A diffusion is denoted as harmful if asignificant life-time reduction of the emitted light can be observed.Standard OLED devices according to state of the art achieve shelf lifetimes in the order of 100000 hours or more. A significant reductiondenotes a reduced life-time of about a factor of 2 or more.

In another embodiment the spacer means has a shape suitable to preventthe emergence of a shadowing edge on a substrate electrode. Thepreferred deposition technology for the organic layers and the counterelectrode on top of the spacer means is vacuum evaporation. Vacuumevaporation is a deposition technology, where the materials to bedeposited follow a straight path from the evaporation source to thesubstrate, leading to a directed deposition. If the spacer means hassteep edges or overhanging edges, shadowing effects will occur, whichlead to holes in the organic layers and the counter electrode. Toprevent this undesirable effect, it is preferable that the spacer meanshas smooth and non-steep edges. As an example, a material propertypreventing the emergence of a shadowing edge is the viscosity, e.g. theviscosity at enhanced temperature. Preferably the viscosity of thematerials of the spacer means is low. If non-conductive glue is used asspacer means it may be applied like a drop onto the substrate electrode.If this non-conductive glue has a viscosity that enables it to flow, asmooth hill-like shape of the spacer means will result, which preventsshadowing effects. If a material is used for the spacer means that givesrise to steep edges that may create shadowing effects if only onedeposition source is used, several deposition sources could be used todeposit material from different directions onto the substrate. It mayalso be advisable to rotate or otherwise move the substrate duringdeposition to ensure a continuous layer deposition over the spacermeans.

In another embodiment the scattering means are pigments and/or flakesand/or particles embedded in the spacer means, preferably aluminumflakes, mica effect pigments or titan dioxide particles. The lightscattering means may be also other flakes or particles known to a personskilled in the art to scatter and/or reflect the artificial light of theorganic electroluminescent device within the scope of this invention.

In another embodiment at least one electrically conductive contact meansis arranged on top of the counter electrode covering an area fully abovethe area of the spacer means suitable to provide an electricalconnection between the counter electrode and a power source through theencapsulation means, which is partly conductive or comprises at leastone electrical feed through suitable to connect the counter electrodewith the power source. This electrical connection between the contactmeans and the encapsulation means may be direct or indirect. In apreferred embodiment the contact means is at least one element of thegroup of conductive glue, spring, arc-shaped spring, rounded tip, pin orcombinations thereof. In a preferred embodiment the conductive glue isanhydrous and/or water free.

As an example of a direct connection, the encapsulation means has directcontact with the conductive glue as the contact means. As an example ofan indirect connection, a means like a wire may be used to connect theencapsulation means and the conductive glue as the contact means. Apartfrom the named wire other means may be used to connect the encapsulationmeans and the contact means, which are known to a person skilled in theart. It is possible to connect the electroluminescent device to anelectrical source with the help of the encapsulation means. Therefore, awire etc. may be attached to the encapsulation means, which transfersthe electrical current via the conductive glue of the contact means tothe counter electrode. Therefore the encapsulation means has to beconductive at least in some parts. To prevent shorts, the encapsulationmeans has then to be insulated against the substrate electrode. Forexample the encapsulation means may comprises an electrically conductivegas-tight feed through. This gas-tight feed through comprises aconductive element, which is directly or indirectly connected to thecontact means. If the encapsulation means is electrically conductive andconnected to the substrate electrode it is preferred that the gas-tightfeed through is electrically insulated against the encapsulation means.This may be done by an insulation means in which the conductive elementis embedded. This insulation means for the gas-tight feed through mayfor example be formed by glass or ceramic, encasing the conductiveelement.

Alternatively the encapsulation means comprises an electricallyconductive contact area. Here, the encapsulation means consists of twodifferent elements, one forming the contact area and another one formingan insulating area. Preferably, the contact area is arranged on top ofthe encapsulation means. Alternative, the contact area may be formed byan element embedded in the encapsulation means, wherein this embeddedelement is conductive. For example a metal disk may be embedded in agas-tight multilayer structure, forming the encapsulation means. Thismetal disk then forms the contact area, which is in electrical contactwith the contact means of the electroluminescent device. Preferably, thecontact area is electrically insulated against the encapsulation means.This may be done by embedding the contact area in glass or ceramic oranother material known to a person skilled in the art.

The invention further relates to a method to provide anelectroluminescent device according to the present invention comprisingthe steps of

-   -   depositing at least one spacer means, preferably a suitable        number of spacer means, with a height adapted to mechanically        support the encapsulation means comprising light scattering        means on top of the substrate electrode,    -   depositing the electroluminescent layer stack on top of the        substrate electrode and the spacer means,    -   depositing the counter electrode on top of the        electroluminescent layer stack, and    -   encapsulating at least the electroluminescent layer stack with        the encapsulation means.

The suitable number of spacer means depends on size and material of theencapsulation means. To prevent the encapsulation means from touchingthe counter electrode in areas with no spacer means underneath, thenumber of spacer means and the distance between adjacent spacer meanshave to be adapted to the area size of the encapsulation means and thelight emitting layer stack. A larger area size requires a higher numberof spacer means. Typically, for a 0.7 mm thick glass cover plate,spacers should be applied every 20 mm. The height of the spacer meanswill be adapted to the distance between substrate electrode and innerside of the encapsulation means and the thicknesses ofelectroluminescent layer stack and counter electrode. The most reliablesupport of the encapsulation means will be achieved by spacer means withheights of essentially equal to the distance between substrate electrodeand encapsulation means minus the layer thicknesses ofelectroluminescent layer stack and counter electrode prepared on top ofthe spacer means.

Another embodiment of the method comprising the further step ofdepositing a contact means, preferably a conductive glue, covering anarea fully above the area of the spacer means on top of the counterelectrode to provide an electrical connection between the counterelectrode and a power source through the encapsulation means beforeapplying the step of encapsulating with an encapsulation means, which ispartly conductive or comprises at least one electrical feed throughsuitable to connect the counter electrode with the power source. Theconductive means may provide a direct or indirect electrical contact tothe corresponding at least partly conductive encapsulation means.Preferably, the contact means is conductive glue and fills the small gapbetween the counter electrode above the spacer means and the inner sideof the encapsulation means to provide a direct electrical contact to theencapsulation means.

The invention further relates to the use of an array, preferably ahexagonal array, of non-conductive spacer means on top of the substrateelectrode for an electroluminescent device with a substrate and anencapsulation means for supporting the encapsulating means, where thespacer means comprise light scattering means for redirecting at least apart of the light trapped in the substrate providing a reliableelectroluminescent device with more homogeneous brightness distributionand an improved light emission.

The aforementioned electroluminescent device and/or method, as well asclaimed components and the components to be used in accordance with theinvention in the described embodiments are not subject to any specialexceptions with respect to size, shape, material selection. Technicalconcepts such that the selection criteria are known in the pertinentfield can be applied without limitations. Additional details,characteristics and advantages of the object of the present inventionare disclosed in the dependent claims and the following description ofthe respective figures—which are an exemplary fashion only—showing aplurality of preferred embodiments of the electroluminescent deviceaccording to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Further embodiments of the invention will be described with respect tothe following figures, which show:

FIG. 1: a side view of an electroluminescent device according to theinvention,

FIG. 2: a side view of an electroluminescent device according to theinvention comprising an array of spacer means redirecting light,

FIG. 3: front view of an electroluminescent device

-   -   (a) according to prior art and    -   (b) according to the present invention comprising spacer means        with scattering means, and

FIG. 4: a side view of the electroluminescent device according to theinvention with contact means to be connected to a power source via theencapsulation means.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 shows an electroluminescent device 10 (OLED) according to thepresent invention comprising a substrate 40 and on top of the substratea substrate electrode 20, a counter electrode 30, an electroluminescentlayer stack 50 and an encapsulation means 90. The electroluminescentlayer stack 50 is arranged between the substrate electrode 20 and thecounter electrode 30 comprising at least one organic light emittinglayer. The electroluminescent layer stack has a thickness of typically100-200 nm. The substrate electrode 20 is formed by an approximately 100nm thick layer of ITO, which is a transparent and conductive material.On top of the substrate electrode 20 a spacer means 70 comprisingscattering particles as the scattering means 80. For example thescattering particles 80 may be Aluminum particles with diameters ofabout 1 micrometer. Onto the substrate electrode 20 and the spacer means70, the organic electroluminescent layer 50 and subsequently the counterelectrode 30 are deposited. If a voltage is applied between thesubstrate electrode 20 and the counter electrode 30 some of the organicmolecules within the organic electroluminescent layer 50 are exited,resulting in the emission of artificial light, which is emitted by theelectroluminescent layer 50. The counter electrode 30 is formed by alayer of aluminum of typically 100 nm thickness, working as a mirrorreflecting the artificial light through the substrate electrode 20 andthe substrate 40. To emit light into the surrounding, the substrate 40in this embodiment is made of glass. Thus, the electroluminescencedevice according to FIG. 1 is a bottom emitting OLED. In case of atransparent counter electrode, e.g. made of transparent ITO or a thin Agor Au layer, the electroluminescent device may be arranged as a top ortransparent emitter using a glass plate as the encapsulation means. Theelectroluminescence device 10 shown in the following figures as well asits components and the components used in accordance with the inventionare not shown true to the scale. Especially the thickness of theelectrodes 20, 30, organic electroluminescent layer stack 50, thesubstrate 40 and the spacer means 70 are not true to the scale. Allfigures just serve to clarify the invention.

If the encapsulation means 90 touches the counter electrode 30 as aresult of an applied force 75 to the encapsulation means 90, e.g. due toan increased atmosphere pressure or other mechanical forces liketouching the backside of the OLED with fingers or tools, the height 72of the spacer means, being significantly larger than the total thicknessof the layers prepared on top of the substrate electrode, limits thearea of the counter electrode touched by the encapsulation means 90 tothe areas of the counter electrode covering the spacer means 70. Theelectrically non-conductive spacer means 70 arranged between bothelectrodes prevent any electrical contact between counter electrode 30and substrate electrode 20. The area 71 on the substrate electrode 20covered by the spacer means 70 (electrically protected area) exceeds thearea on the counter electrode 30 being in contact with the encapsulationmeans 90 (support area). The spacer means 70 isolates the substrateelectrode 20 from the counter electrode 30 and any parts of the counterelectrode 30, which may be damaged by a mechanical contact with theencapsulation means 90 and may penetrate the organic electroluminescentlayer 50, but will not be in any contact to the substrate electrode 20.To provide a mechanical support to the encapsulation means preventinglarger movements of the encapsulation means towards the layer stack, theheight of the spacer means 72 may be adapted to be essentially the sameas the distance 92 between the counter electrode 30 and the inner side92 of the encapsulation means 90 as present outside the area coveredwith spacer means, preferably the encapsulation means 90 is a flat lid.

The spacer means 70 has to have material properties and/or applicationprocedure that prevents the emergence of a shadowing edge on thesubstrate electrode 20. In a preferred embodiment the material propertyis low viscosity. Therefore, the material forming the spacer means willflow on the substrate electrode 20, forming a hill-like structure withsmooth slopes. There will be no shadow edges, which could disturb acontinuous coverage of the organic electroluminescence layer 50 and thecounter electrode 30, especially the electroluminescent layer stack 50and the counter electrode 30 can be prepared without cracks, voids orother defects in the area around the spacer means 70. The spacer means70 preferably has a lower viscosity at enhanced temperature that enablesa two step application. In a first step the material forming the spacermeans—like non-conductive glue—is applied to the substrate electrode 20in the desired position. Then the substrate is heated to an enhancedtemperature. Due to its lower viscosity, the material of the spacermeans 70 will then flow out on the substrate electrode 20. Preferablythe material of the spacer means 70 comprises a viscosity that enablesit to flow slowly, to form a spacer means 70 with a defined height andsmooth slopes. As the temperature of the spacer means and/or thematerial of the spacer means decreases, it should solidify, to form thespacer means 70. This ability and/or material property of the spacermeans 70 to flow onto the substrate electrode 20 in such a way, that noshadowing edges are formed enables the manufacturing of the disclosedelectroluminescence device 10

FIG. 2 shows an encapsulated electroluminescent device 10 according tothe present invention. A driving voltage will be applied to theelectroluminescent device between the areas of the substrate electrodenot covered with spacer means 70 and the counter electrode leading tolight generation in the electroluminescent layer stack 50 andsubsequently leading to the emission of light 60 from these areasbetween the spacer means 70. Due to the optical properties of theelectroluminescent layer stack, substrate electrode and substrate, amajor part of the generated light will not be coupled out to theenvironment but is trapped within the substrate as trapped light 61. Thescattering means 80 embedded in the spacer means 70 redirects asignificant part of the light 61 trapped within the substrate 40 towardsthe substrate surface with an angle of incidence suitable forout-coupling of light 65 to the environment. The shownelectroluminescent device 10 comprises an encapsulation means 90, whichinner side 91 is in contact to or arranged close to the counterelectrode 30 supported by the spacer means 70. The encapsulation means90 is attached to the substrate electrode 20 in a gas-tight manner, e.g.with glass frit, or glue, or metal solder, to seal theelectroluminescent layer stack 50 from harmful gases such as waterand/or oxygen. To prevent an electrical contact between counterelectrode 30 and substrate electrode 20 via the encapsulation means (incase of occasionally or permanently contact between encapsulation meansand counter electrode), the encapsulation means must have either anisolating inner side 91 or an isolation top body 95 or isolating sides96. Alternatively, the whole encapsulation means by electricallynon-conductive (=isolating).

FIG. 3 shows front views of electroluminescent devices from thesubstrate side: (a) according to prior art and (b) according to ourpresent invention. The spacer structure 110 covering the shunt lines ofthe prior art device (a) supports the encapsulation means on thebackside of the device (not shown here), but the spacer structure 110 isvisible to a viewer through the substrate 40 as black lines 110. Incontrast to prior art, the electroluminescent device (b) according tothe present invention provides an appearance with almost homogeneousbrightness. The spacer means 70 are shown as small (dashed) circles in ahexagonal array, which is a geometry less sensitive to the human eye.The dashes circles shall indicate the less visibility of the spacermeans 70, in case of carefully adapted scattering properties thenon-visibility of the spacer means 70. As an example, an array of spacermeans 70 were made of a two-component epoxy glue (UHU plus schnellfest,curing time 5 min) The binder of the glue was mixed with TiO₂ scatteringparticles as the scattering means, leading to a white substance. Thebinder and the hardener were mixed in the prescribed ratio of 1:1 andthen applied at room temperature to the ITO-covered glass substrate inone spot. Then the substrate was heated on a hot plate to 60° C. for 15min, which allowed the glue first to flow into a smooth hill and then tosolidify rapidly. The procedure was carried out in a glove box in dryNitrogen atmosphere (less than 1 ppm of water). The substrate with thehardened spacer means 70 was then introduced into a vacuum chamber andthe electroluminescent layer stack 50 and the counter electrode 30 weredeposited. The finished device was then encapsulated with a glass coverlid 90. A getter for water may be placed in the cavity formed by thesubstrate 40 and the lid 90. After setting of all glues (appr. 1 hour),the electroluminescent device was reliably driven. Theelectroluminescent layer stack 50 and the counter electrode 30 made ofAluminum covered the spacer means without cracks or holes. At theposition of the spacer means, a light emission due to the scattering ofthe light guided in the substrate by the TiO₂ particles embedded in theglue made the spacer means almost invisible compared to the emittingareas not covered by spacer means 70. The resulting electroluminescentdevice was not sensitive to forces applied to the cover lid supported bythe spacer means 70.

The brightness of the areas 71 covered by spacer means 70 can be adaptedby choosing suitable scattering materials (reflectivity, refractiveindex) added to the spacer means 70 as particles and/or flakes, suitableamount and size of such particles and/or flakes. To further enhance thescattering effect, the substrate may comprise additional scatteringmeans above the spacer means. People skilled in the art are able toselect suitable particle and/or flake concentration and theircorresponding sizes in order to adapt the brightness of the areascovered by the spacer means to the desired value, preferably to abrightness equal to the brightness of the surrounding areas of theelectroluminescent device making the spacer means invisible to theviewer within the scope of this invention.

FIG. 4 shows the electroluminescent device according to the presentinvention as shown in FIG. 1 with additional conductive glue as thecontact means 100 on top of the counter electrode 30 covering an areafully above the area 71 of the spacer means 70 providing an electricalconnection between the counter electrode 30 and a conductive part 97within the top 95 of the encapsulation means 90 further connected to apower source via a connection 93. In this embodiment, the contact means100 is directly connected to the conductive part 97 of the encapsulationmeans 90. The conductive part 97 is one example of possible electricalfeed through providing an electrical connection from a power sourcethrough the encapsulation means to the counter electrode. Alternatively,there may be a wire feed through electrically isolated against the top95 of the encapsulation means. Alternatively the top 95 of theencapsulation 90 may be completely conductive and isolated against thesubstrate electrode via a non-conductive side 96 of the encapsulationmeans 90. In this embodiment, a conductive part 97 as shown in FIG. 4 isnot required. The contact means may also be in a non-direct contact tothe encapsulation means via conductive springs, arc-shaped springs,rounded tips, pins or combinations thereof.

As an example, conductive glue (Circuitsworks conductive epoxy CW2400from Chemtronics Inc.) can be applied though a hole in the encapsulationmeans 90 to the counter electrode 20 at the position of the spacer means70 and a metal plate 97 was attached with two component epoxy to the top95 of the encapsulation means 90, closing the hole in the encapsulationmeans 70 in such a way that the side of the metal plate 97 facingtowards the counter electrode 30 is at least partly covered by theconductive glue 100. After setting of all glues (approximately 1 hour),the OLED was reliably driven by connecting the plus lead of a powersupply to the rim of the substrate where the substrate electrode wasexposed and the minus lead to the metal plate 97 on the encapsulationmeans 90.

The described embodiments comprise as an example one organicelectroluminescent layer 50 within the electroluminescent layer stack50. In alternative embodiments within the scope of this invention, theelectroluminescent layer stack may comprise additional layers such ashole transport layers, hole blocking layers, electron transport layers,electron blocking layers, charge injection layers further conductinglayers etc.

LIST OF NUMERALS

-   10 electroluminescent device-   20 substrate electrode-   30 counter electrode-   40 substrate-   50 electroluminescent layer stack-   60 light emitted from areas non-covered by spacer means-   61 light trapped within the substrate-   65 light emitted from areas covered by spacer means-   70 spacer means-   71 area covered by spacer means-   72 height of spacer means-   75 force applied to encapsulation means-   80 scattering means-   90 encapsulation means-   91 inner side of the encapsulation means-   92 height of encapsulation means above the substrate electrode-   93 connection to power source-   95 top of encapsulation means-   96 side of encapsulation means-   97 electrical feed through-   100 contact means-   110 spacer lines according to prior art

The invention claimed is:
 1. An electroluminescent device comprising asubstrate and on top of the substrate a substrate electrode, a counterelectrode and an electroluminescent layer stack with at least oneorganic electroluminescent layer arranged between the substrateelectrode and the counter electrode, an encapsulation meansencapsulating at least the electroluminescent layer stack and at leastone non-conductive spacer means arranged on the substrate electrode tomechanically support the encapsulation means and to prevent anelectrical short between the substrate electrode and the counterelectrode during the mechanical support, wherein the spacer meanscomprise at least one light scattering means that is dispersed withinthe spacer means and wherein the spacer means functions to enhanceoutput, from the device, of light trapped in the substrate by scatteringat least a portion of the light trapped in the substrate with saidscattering means.
 2. The electroluminescent device according to claim 1,wherein the sum of all areas covered by the spacer means on top of thesubstrate electrode is less than 10% of the area covered by theelectroluminescent layer stack.
 3. The electroluminescent deviceaccording to claim 1, wherein the largest extension of the area coveredby the spacer means is less than 10% of each of the lateral extensionsof the area covered by the electroluminescent layer stack.
 4. Theelectroluminescent device according to claim 1, wherein theelectroluminescent device comprises an array of spacer means.
 5. Theelectroluminescent device according to claim 1, wherein the spacer meanshas a height ranging between 5 and 1000 micrometer.
 6. Theelectroluminescent device according to claim 5, wherein the height ofthe spacer means is adapted to be essentially the same as the distancebetween the counter electrode and the inner side of the encapsulationmeans as present outside the area covered with spacer means.
 7. Theelectroluminescent device according to claim 1, wherein the spacer meanscomprises at least one of the following materials: non-conductive glue,a photo resist, a lacquer, paint or a layer of glass, made of re-meltedglass frit or combinations thereof.
 8. Electroluminescent deviceaccording to claim 7, wherein the non-conductive glue of the spacermeans is anhydrous and/or water free.
 9. The electroluminescent deviceaccording to claim 1, wherein the space means has a shape suitable toprevent the emergence of a shadowing edge on a substrate electrode. 10.The electroluminesce device according to claim 1, wherein the scatteringmeans are pigments and/or flakes and/or particles embedded in the spacermeans.
 11. The electroluminescent device according to claim 1, whereinat least one electrically conductive contact means is arranged on top ofthe counter electrode covering an area fully above the area of thespacer means suitable to provide an electrical connection between thecounter electrode and a power source through the encapsulation means,which is partly conductive or comprises at least one electrical feedthrough suitable to connect the counter electrode with the power source.12. The electroluminescent device according to claim 11, wherein thecontact means is at least one element of the group of conductive glue,spring, arc-shaped spring, rounded tip, pin or combinations thereof.